If they can get out, they have a chance. There was a crash on the Potomac in January 1982 and there were several survivors. The video of the rescue is pretty crazy.
There was a truck that crashed on bridge right next to lincoln memorial and then veered off roadway into bridge, and both were deceased. Its very cold in DC right now and an airplane crashing is much more catastrophic.
It was very cold in DC until recently but it's 45°F right now at 11:21. I was walking & biking around in a sports jacket today with a winter coat strapped onto the outside of my bag.